U.S. Pat. No. 4,271,379 discloses a web fed press with two press units, each including a driving means driven by a motor. Each motor has an encoder that produces pulse trains corresponding to the positioning of the motor. These pulse trains are compared by a phase comparator, producing a voltage that passes through a filter amplifier and is level shifted by a level shifting circuit, which outputs a signal that represents the speed error between the motors. The signal then passes through a proportional amplifier, an integrator amplifier, two summing input resistors and a summing amplifier, to a regenerative drive circuit. If the relationship between the speed of the motors is not as desired, the energization of the second motor is corrected by the regenerative drive circuit to achieve the proper speed relationship.
U.S. Pat. No. 5,894,802 discloses a method and apparatus for providing disturbance-free speed and position reference signals to drive shafts in a printing press. An isolated position reference unit receives a signal indicating the desired speed of a printing web and generates isolated position reference signals. The position reference signals and are then sent to speed controllers that control the speed of the drive shafts accordingly. Position encoders determine the position of the drive shaft. Regulators then correct the isolated position reference signal based on the determined drive shaft position.
U.S. Pat. Pub. 2006/0267529 discloses an apparatus for use with an encoder feedback device including a comparator, a counter, and a prediction unit. An encoder includes a scanner and determines the position of a rotating load by identifying radially displaced optical markings disposed about the periphery of a disk that is coupled to and rotates with the load. The encoder then sends sine/cosine signals indicating the position of the load to the comparator, which converts the signals into square waves. The counter then counts the rising and falling edges of the square wave signals and stores a position value that represents the position of the load at a certain time. The prediction unit then receives the position value from the counter at a certain time and predicts the position of the rotating load at that time as a function of at least a subset of the position values generated prior to that time and a misalignment between that time and a predetermined update interval to generate an aligned position signal.
U.S. Pat. Pub. 2007/0013334 discloses an electronic line shaft system with master controller that includes a predictor for anticipating a position value of an encoder at a fixed future time. The encoder measures the position of the master line shaft and sends a position signal to the master controller. The master controller, after receiving a command signal from a virtual encoder, then sends a position signal to the predictor, which anticipates the position value of the encoder at a fixed future time. This predicted position value is sent to servant motor drives that hold the predicted position value until a strobe signal sent by the predictor causes each of the servant motor drives to accept the predicted position value and to control their motor systems accordingly. This allows the line shafts driven by the motors to synchronize their positioning.